A critical issue for manufacturers of coating equipment is the need to meet customer demands for increased efficiencies in the coating application process. Regardless of the coating type or application methodology, uniformity of application and transfer efficiency are critical parameters that continue to be addressed by research and development efforts.
Selection of the appropriate application methodology depends not only on the type of coating but also on the requirements of the substrate to which it is applied.
For example, where the acoustical capabilities of an object are sought to be maintained, it is widely known in the coatings art that it is critical for the coating to have little or no impact on acoustical performance of the material, i.e. the coating is acoustically transparent. It is also widely known that the acoustical performance of a material is impacted by both the uniformity of application as well as the thickness of the coating. Thus, obtaining the optimal performance of a material, such as an acoustical fibrous mat, requires a minimum deviation of acoustic capability across the entire surface of the material.
One well known large-scale, i.e. industrial-scale, atomization technique which provides acoustical transparency and wide-area coverage is illustrated in prior art FIG. 1. This conventional large-scale coating technique utilizes a series of single-point atomizing spray guns, or nozzles. This system is commonly known in the industry as an overlap, or multi-tip header. As shown in FIG. 1, each nozzle 1A-1E, commonly referred to in the art as a single-point nozzle, produces an atomized fluid stream, 3A-3E respectively, which spreads out, or diverges, into a conical spray pattern. To ensure complete coverage across a large width, the outer portions of the atomized fluid streams 3A-3A must overlap. Though undetectable to the naked eye, these overlapping streams do not uniformly apply the coating.
To approach uniformity of application using overlap header technology, several features can be manipulated, including: the spacing of the nozzles; the spacing between the overlap header and the object to be coated; the tip geometry of the nozzles; and the flow rate of the fluid passing through the nozzles. However, it is widely known and understood by those of ordinary skill in the art that overlap header technology assumes a density gradient for each nozzle, and, thus, the effort to approach uniformity of application is an iterative process that is fundamentally variable.
One skilled in the art further understands that it is impossible to completely eliminate defects such as streaks and shade variation using an overlap header. A conventional attempt to randomize these defects is to use cyclically traversing, i.e. reciprocating, multi-tip headers instead of multi-tip fixed headers. Conventional wisdom is that randomizing these defects will in effect disguise the defects and make them undetectable to the naked eye.
Unfortunately, both fixed and reciprocation headers add cost to the final product. For example, as the tip of each gun gradually wears or even becomes clogged, the spray pattern of the gun will change and ultimately lead to a more non-uniform application. Also, frequent interruptions due to cleaning or replacement of the tips adds considerable expense in terms of the downtime required and the cost of the replacement part. Thus, an alternative large-scale technique which addresses the issues with existing techniques is needed.